This invention relates to a stamped knitting tool for textile machines, particularly knitting machines and is of the type which has a shank carrying at least one butt and being provided with at least one free space (also referred to hereafter as "window") which is filled with a heterogenous material, particularly a plastic material fixedly secured to the shank.
By "knitting tools" there are meant latch needles, springbeard needles, compound needles, latchless needles (for example, hooks for working on plush material), as well as sinkers and the like.
German Patent No. 3,314,809 discloses a stamped knitting tool of the above-outlined type wherein at least one window is provided in the tool shank; the window is constituted by an elongated opening whose longitudinal axis is parallel to or coaxial with the longitudinal shank axis. The elongated aperture is bordered by two vertical guiding parts extending from the upper shank edge to the lower shank edge and two narrow webs which interconnect the guiding parts and which are oriented parallel to one another. The window is filled with a vibration damping material which is fixedly connected with the needle shank. The vibration damping material is, as a rule, an elastic plastic having substantial damping properties; yet, the use for other materials is not excluded. The above-noted German patent describes several embodiments having one or more windows enclosed by the webs and guiding parts.
The oscillation damping material disposed in the window or windows, as it has been found in practice, advantageously affects the vibration behavior of the knitting tool. It is possible to provide the knitting tool with a highly elastic construction having web heights of maximum 1.1 mm and to use the knitting tools over long operational periods with high working speed without experiencing, to an appreciable extent, web fractures caused by metal fatigue or hook breakages.
Since the oscillation damping material that fills the window in the needle shank may be effective only if it is fixedly connected with the material of the shank along the edge of the window, particularly in case of very thin needles which in the zone of the window are exposed to bending by laterally attacking forces, additional measures have been taken to ensure a form-fitting anchoring of the plastic filler in the window. Thus, European Published Application 0 282 647 discloses that the web parts or guiding parts which bound the window are given a particular shape (profile). Such a shape may have regions of reduced wall thicknesses which are either arranged in a locally limited manner or extend as strips over the entire outline of the window or a part thereof. Such regions of reduced wall thickness extend into the plastic material that fills the window and contribute to its form-fitting anchoring to the shank.
It has been found in practice that the making of knitting tools, particularly needles having windows provided therein which along the window-framing edges of the shank have profiled zones of reduced shank thickness are relatively difficult to make and are relatively expensive. For forming such an anchoring means for the plastic material, particularly made stamping tools are required and, especially in case of windows bounded by webs of small height, precautions have to be taken to prevent drawing of the thin webs during manufacture. The zones of reduced shank thickness adjoining over the rectangular shoulder zones at the shank may lead, at high dynamic stresses of the knitting tool, to locally limited stress peaks which adversely affect the service life of the knitting tool.